The present invention relates to a starter for an engine, particularly to the improvement of a motive power transmission system extending from an electric motor to a pinion in a starter for starting the engine of a vehicle.
FIG. 2 shows a conventional starter 1 which is of the so-called side mount type and used to start the engine of a vehicle. The starter 1 comprises a DC motor 2, an output rotary shaft 3 extending in parallel with an armature shaft 2a of the DC motor, a speed reduction gear 4 engaged with a gear 2b provided on the armature shaft, an overrunning clutch 5 slidably supported on the output rotary shaft, a pinion 6 integrated or coupled with the inner member (not shown in the drawing) of the overrunning clutch and a shift lever 8 which is engaged at one end thereof with the actuation rod 7a of an electromagnetic switch 7 disposed alongside the DC motor and is engaged at the other end thereof with the overrunning clutch, to slide the clutch together with the pinion on the output rotary shaft. Since the number of the teeth of the pinion 6 is made as many as about twenty due to the restrictive condition of the mounting of the starter on the vehicle although the number of the teeth of the pinion of an ordinary starter is about eight, the torque transmitted to the engine by the starter shown in FIG. 2 is relatively low. For that reason, the speed reduction gear 4 is used to increase the speed reduction ratio of the starter to heighten the transmitted torque. However, the increase in the speed reduction ratio is not large enough. It is conceivable that either the torque of the DC motor 2 or the internal speed reduction ratio of the starter is increased in order to heighten the torque transmitted to the engine by the starter. However, increasing the torque of the DC motor 2 is not preferable because it results in making the starter heavier or larger. Besides, increasing the internal speed reduction ratio of the starter is also not preferable because it results in greatly augmenting the number of the parts of the starter to make the manufacturing of the starter more troublesome and the cost thereof higher. This is a problem.